> Operationally, knowing how the system will react to extreme conditions might be more valuable than being a little more optimal.

But there's a lot of theory around PID control to show how PID control systems behave under all sorts of circumstances. Hell, there's even things that are mathematically provable, like for example stability, which I strongly suspect you may often not even be able to reason about in case of many an ad-hoc systems like the ones GP is talking about.